The present invention relates to a low-temperature fuel cell assembly comprising a fuel cell having a sweeping gas circuit for fuel gas, said sweeping gas circuit being connected to the inlet and outlet of the anode of the fuel cell and supply means being provided for fuel, which is connected to said sweeping gas circuit via a physical separation device, means being arranged in the sweeping gas circuit for producing sweeping gas therein.
A low-temperature fuel cell of this type can be an SPFC cell (solid polymer fuel cell), but it must be understood that this term is also understood to cover any other low-temperature fuel cell, such as a phosphoric acid fuel cell. Low temperature is understood to be an operating temperature of below 200° C. In the case of an SPFC cell, the fuel gas used is frequently hydrogen and hydrogen is obtained by a reforming reaction, for example from methane. Admission to the fuel circuit takes place through a semi-permeable wall or corresponding technique such as sorption, hydrogen atoms/molecules being allowed to pass through, but not other gases. In order to optimise the passage through such a semi-permeable wall it is proposed in the prior art to use a sweeping gas in the fuel supply. This sweeping gas must preferably be inert, is not itself consumed in the fuel cell and is largely recycled. It is for this reason that a sweeping gas circuit is present. As a result of the use of the sweeping gas the concentration of hydrogen or other fuel gas is lower and accelerated passage through the semi-permeable wall or other filter will take place, whilst sufficient hydrogen is admitted for operation of the fuel cell.
An assembly of this type is disclosed in U.S. Pat. No. 5,976,724. In this assembly the anode gas is supplied via a semi-permeable membrane to a closed anode circuit. In this assembly water is used as sweeping gas. This sweeping gas is generated by evaporation of water present in the circuit as a liquid, which is condensed before entry into the anode.
As far as the sweeping gas is concerned, such a circuit is completely closed. It has been found that poisoning of the sweeping gas occurs during long-term use of such a fuel cell assembly, as a result of which the efficiency of the fuel cell falls (dramatically).